<p>This paper intends to analyze the determinants of audit fees in Portugal and Spain at a time when the audit profession has felt increasingly strong pressures on its ethical, independence and quality posture, showing that audit fees behave differently in these two countries. The liberalization of audit services in Portugal, with the elimination in 2005 of the table setting the minimum fees based on the size standards of the audited company, arouses the interest in perceiving the factors that determine audit fees. In Spain, the various financial scandals have placed audit fees in the main focus. These countries, which form the Iberian Peninsula, have a strongly related economic and cultural history, having also joined the European Union on the same date. In addition, audit fees have not been much studied in these countries, so it is important to perceive their behavior by comparing results. The results indicate that, in Spain, audit fees are determined mainly by the size, complexity and risk of the audited company. It was also found that in Spain the big four companies charge higher fees and that companies that change their audit firm pay lower fees in the year of rotation. In Portugal, the size of the audited company was considered the only factor contributing to the determination of audit fees. The analysis includes a sample of 39 listed companies in Portugal and 104 companies listed in Spain for the period of 2013 to 2015 using the ordinary least squares.</p>